I must agree, WiseBobo sometimes showes some qualities of scaryness...
The MP40 is for sure the "Burp Gun".... today I've watched a few movies with shooting of firing with an MP40 (home-made video). It is more like a heavy wind blowing with a lot of sparkles going trough, but that makes the "burping" effect.
I also saw that episode of Mail Call. Right when i saw the forum i thought of the "grease gun."Im not sure unleashed might be quite right. The grease gun was a cheap gun bought the US to replace the Thompson because the cost of Thompsons were a lot more. The "grease gun" had a retractable stalk. The soldiers at first did not like the grease gun but then started to get use to it and said that it was much more lighter that the Thompson. Im sure u recall all this information vortex from that episode.